Identifying hexagonal boron nitride monolayers by transmission electron microscopy.

Multislice simulations in the transmission electron microscope (TEM) were used to examine changes in annular-dark-field scanning TEM (ADF-STEM) images, conventional bright-field TEM (BF-CTEM) images, and selected-area electron diffraction (SAED) patterns as atomically thin hexagonal boron nitride (h-BN) samples are tilted up to 500 mrad off of the [0001] zone axis. For monolayer h-BN the contrast of ADF-STEM images and SAED patterns does not change with tilt in this range, while the contrast of BF-CTEM images does change; h-BN multilayer contrast varies strongly with tilt for ADF-STEM imaging, BF-CTEM imaging, and SAED. These results indicate that tilt series analysis in ADF-STEM image mode or SAED mode should permit identification of h-BN monolayers from raw TEM data as well as from quantitative post-processing.